The present invention relates to the treatment of lead drosses and, more particularly, to the pyrometallurgical treatment of nickeliferous and cobaltiferous lead drosses.
Most lead ores contain significant amounts of arsenic and antimony in addition to other impurities. Lead bullion is produced by roasting the ores and then smelting the roasted ore in a blast furnace. Molten lead bullion from the furnace is charged to primary drossing kettles in which oxides and other insolubles float to the surface of the molten lead at a later stage. Sulfur is then added to the partially drossed molten lead to form sulfides of copper, and other impurities. During this so-called decopperizing stage the molten lead is stirred to insure complete reaction between the sulfur and the copper. Once the decopperizing reactions are completed the sulfides formed are allowed to float to the surface of the bath, and the refined lead bullion and the sulfur dross are then separated. The sulfide dross obtained in this stage can be recycled to either the blast furnace or to the primary drossing kettles but in either case the dross from the primary drossing kettles is conventionally smelted in a reverberatory furnace to recover additional amounts of lead and to recover copper and other metals in the form of matte and/or speiss which can be treated by copper smelters.
Lead ores mined in the southeastern portion of Missouri are unusual in that they contain significant quantities of nickel and cobalt as well as arsenic and copper. These characteristics of southeastern Missouri lead ores cause problems in the treatment of the lead refining kettle drosses resulting therefrom. The presence of significant quantities of nickel and cobalt result in the formation and the precipitation on the furnace sidewalls of high melting point nickel-and cobalt-containing speisses. The continual buildup of these deposits in a conventional dross smelting furnace, such as a reverberatory furnace, gradually reduces the capacity of the furnace and ultimately forces furnace shutdown for removal of the deposit.